Compact Framework - Using the Treeview to replace the ListBox

Tim Mackey — Wed, 26 May 2010 14:51:34 GMT

As any compact framework developer will tell you, the out-of-the-box ListBox control is a bit crap because it doesn't support horizontal scrolling. what were they thinking??
anyway, after several work-arounds to this problem, i finally realised that the treeview control does support horizontal scrolling, and you can load up a treeview to look just like a listbox, having all the nodes added at the top level, i.e. a "flat" treeview.
the extra bonus with this approach is that Windows Mobile 6.5 has a brilliant touch friendly Treeview control that you can finger-drag up and down and left and right (at least the HTC HD2 has this, i can't vouch for other devices).

i've included a "Chooser" class i wrote to make user selections easy to code for. to use the class, use the following approach, the SelectedItem string is kept as a static variable in the Form so you can close and dispose the form straight away, and still catch the "return" value of the form. If you pass in the parameter to use Checkboxes, you can access the CheckedItems static property which is a List<string>.

Chooser c = new Chooser("Select Item", new string[]{"Option 1", "Option 2", "Option 3"}, true, true); 


DialogResult d = c.ShowDialog();

c.Dispose();

if(d != DialogResult.Cancel)

MessageBox.Show("You chose " + Chooser.SelectedItem);

here's the class then:

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Text;

using System.Windows.Forms;

using System.Threading;



namespace IbenzaMobileUtil

{

public partial class Chooser : Form

{

private MainMenu mainMenu1;

private MenuItem mmOK;

private MenuItem mmCancel;

private Label lblCaption;

public static string SelectedItem = null;

public static List<string> CheckedItems = null;

private TreeView treeView1;

private bool selectInvokesClose;





public Chooser()

{

InitializeComponent();

}



private Chooser(string Caption, bool FullScreen, bool SelectInvokesClose)

{

InitializeComponent();

CheckedItems = new List<string>();

SelectedItem = null;

this.selectInvokesClose = SelectInvokesClose;

this.lblCaption.Text = Caption;

this.mmOK.Enabled = false;



if (FullScreen)

{

this.WindowState = FormWindowState.Maximized;

this.FormBorderStyle = FormBorderStyle.None;

this.ControlBox = false;

this.MinimizeBox = false;

}

}



public Chooser(string Caption, string[] Items, bool FullScreen, bool SelectInvokesClose)

: this(Caption, FullScreen, SelectInvokesClose)

{

this.treeView1.BeginUpdate();

foreach (string s in Items)

this.treeView1.Nodes.Add(s);

this.treeView1.EndUpdate();

}



public Chooser(string Caption, string[] Items, bool FullScreen, bool CheckBoxes, bool
SelectInvokesClose, bool CheckAll)

: this(Caption, Items, FullScreen, SelectInvokesClose)

{

this.treeView1.CheckBoxes = CheckBoxes;

if (CheckBoxes && CheckAll)

foreach (TreeNode node in this.treeView1.Nodes)

node.Checked = true;

if(CheckBoxes)

this.mmOK.Enabled = true; // don't require any user input

}



private void treeView1_AfterSelect(object sender, TreeViewEventArgs e)

{

this.mmOK.Enabled = true;

if (selectInvokesClose)

this.mmOK_Click(sender, EventArgs.Empty);

}



#region Windows Form Designer generated code



/// <summary>

/// Required designer variable.

/// </summary>

private System.ComponentModel.IContainer components = null;



/// <summary>

/// Clean up any resources being used.

/// </summary>

/// <param name="disposing">true if managed resources should be disposed; otherwise,
false.</param>

protected override void Dispose(bool disposing)

{

if (disposing && (components != null))

{

components.Dispose();

}

base.Dispose(disposing);

}





/// <summary>

/// Required method for Designer support - do not modify

/// the contents of this method with the code editor.

/// </summary>

private void InitializeComponent()

{

this.mainMenu1 = new System.Windows.Forms.MainMenu();

this.mmCancel = new System.Windows.Forms.MenuItem();

this.mmOK = new System.Windows.Forms.MenuItem();

this.lblCaption = new System.Windows.Forms.Label();

this.treeView1 = new System.Windows.Forms.TreeView();

this.SuspendLayout();

// 


// mainMenu1

// 


this.mainMenu1.MenuItems.Add(this.mmCancel);

this.mainMenu1.MenuItems.Add(this.mmOK);

// 


// mmCancel

// 


this.mmCancel.Text = "Cancel";

this.mmCancel.Click += new System.EventHandler(this.mmCancel_Click);

// 


// mmOK

// 


this.mmOK.Text = "OK";

this.mmOK.Click += new System.EventHandler(this.mmOK_Click);

// 


// lblCaption

// 


this.lblCaption.Dock = System.Windows.Forms.DockStyle.Top;

this.lblCaption.Font = new System.Drawing.Font("Tahoma", 10F, System.Drawing.FontStyle.Bold);

this.lblCaption.Location = new System.Drawing.Point(0, 0);

this.lblCaption.Name = "lblCaption";

this.lblCaption.Size = new System.Drawing.Size(240, 27);

this.lblCaption.Text = "...";

// 


// treeView1

// 


this.treeView1.Dock = System.Windows.Forms.DockStyle.Fill;

this.treeView1.Location = new System.Drawing.Point(0, 27);

this.treeView1.Name = "treeView1";

this.treeView1.ShowLines = false;

this.treeView1.ShowPlusMinus = false;

this.treeView1.ShowRootLines = false;

this.treeView1.Size = new System.Drawing.Size(240, 241);

this.treeView1.TabIndex = 12;

// 


// Chooser

// 


this.AutoScaleDimensions = new System.Drawing.SizeF(96F, 96F);

this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Dpi;

this.AutoScroll = true;

this.ClientSize = new System.Drawing.Size(240, 268);

this.ControlBox = false;

this.Controls.Add(this.treeView1);

this.Controls.Add(this.lblCaption);

this.KeyPreview = true;

this.Menu = this.mainMenu1;

this.MinimizeBox = false;

this.Name = "Chooser";

this.Text = "Choose Item";

this.Load += new System.EventHandler(this.Chooser_Load);

this.KeyDown += new System.Windows.Forms.KeyEventHandler(this.Chooser_KeyDown);

this.ResumeLayout(false);



}

#endregion



private void Chooser_KeyDown(object sender, KeyEventArgs e)

{

if ((e.KeyCode == System.Windows.Forms.Keys.Enter))

this.mmOK_Click(sender, EventArgs.Empty);

}



private void mmOK_Click(object sender, EventArgs e)

{

if (this.treeView1.SelectedNode != null)

Chooser.SelectedItem = this.treeView1.SelectedNode.Text;

if (this.treeView1.CheckBoxes)

foreach (TreeNode n in this.treeView1.Nodes)

if (n.Checked)

CheckedItems.Add(n.Text); 




this.DialogResult = DialogResult.OK;

this.Close();

}



private void mmCancel_Click(object sender, EventArgs e)

{

this.DialogResult = DialogResult.Cancel;

this.Close();

}



private void Chooser_Load(object sender, EventArgs e)

{

this.treeView1.Focus();

this.treeView1.SelectedNode = null;

this.treeView1.AfterSelect += new TreeViewEventHandler(treeView1_AfterSelect);

}

}

}

MultiThreading In CF2 with Delegates

Tue, 09 Oct 2007 14:00:03 GMT

what a frustrating problem this was. delegates weren't support in CF1, but now we have CF2 and according to microsoft:

The .NET Compact Framework 2.0 now supports asynchronous execution of a delegate on a user interface thread. Unlike the .NET Compact Framework 1.0 that supports only the Control.Invoke method (which synchronously executes a delegate on a control's owning thread), the .NET Compact Framework 2.0 provides Control.BeginInvoke that asynchronously executes a delegate on the control's owning thread. The Control.EndInvoke method is also provided. When called, the EndInvoke method returns the results of an asynchronous operation.

This is great but it's easily assumed that delegates are fully supported now in CF2, but no such luck. they don't say that calling BeginInvoke on a delegate will cause your application to crash (with a NotSupportedException) even though it will compile in visual studio without warning or error. there is an excellent (if lengthy) discussion on the matter on this newsgroup post. the long and short of it is that you should use the ThreadPool class instead of using delegates to fire off worker threads. You can still use delegates to send a function back to the UI thread just like in winforms. Notice in the code below that the method signature of the function you are starting the thread on, requires a single 'object' parameter.

using System.Threading;



private void Button_Click(etc)

{

ThreadPool.QueueUserWorkItem(new WaitCallback(this.DoSomeWork));

}



private void DoSomeWork(object o)

{

...

}

Bug in ComboBox SelectedIndex

Tue, 02 Oct 2007 16:17:18 GMT

big bug in ComboBox control here: http://support.microsoft.com/default.aspx?scid=kb;en-us;327244
you have to set the SelectedIndex to -1 twice in a row if you want it to take effect!
i came across this in a compact framework app, but it looks like it applies to win-forms as well.

Tim Mackey's Weblog - .Net Compact

Compact Framework - Using the Treeview to replace the ListBox

MultiThreading In CF2 with Delegates

Bug in ComboBox SelectedIndex